A digital disc, such as musical CD, MD mini-compact disc, CD-ROM, DVD compact disc, etc., is used to store a large amount of digital data in the form of microscopic pits which are formed densely and serially on the digital disc. The digital disc is generally formed with a transparent protective outer layer for protecting the integrity of data stored in the reading area of the digital disc. The digital disc is played on a device using a laser beam to read the encoded information stored on the disc. It is therefore conceivable that a reading distortion may be resulted from a damaged or contaminated protective layer. For this reason, the user of the compact disc is advised to handle the compact disc carefully.
The Taiwan Patent Publication No. 312232 describes an annular strip, as a prior art, for protecting a compact disc in such a manner that the annular strip is attached fixedly to the rim of the compact disc, so as to prevent the reading area of the compact disc from making contact with a surface at such time when the compact disc is placed on the surface by utilizing the height of the annular strip.
The inventor of the Taiwan Patent Publication No. 312232 discloses another structure for protecting a compact disc to improve the annular strip. The structure comprises a protective film which has a thickness of 60 microns (.mu.m) or less. The protective film is adhered by static attraction to the surface of the reading side of the compact disk and is also adhered by adhesive to the inner annular portion thereof. Such a protective film as described above has several drawbacks, which are described hereinafter.
The side of the reading area of the compact disc has a protruded ring surrounding the central hole thereof, which will cause the protective film not being able to be attached flatly to the surface of the reading side, especially at the portion near the protruded ring of the compact disc. As a result, the static attracted portion of the protective film is prone to become detached.
The adhesive can not be easily applied to the inner annular portion of the compact disc in terms of the position and the quantity of the adhesive. In addition, the reading area of the compact disc is vulnerable to contamination by the adhesive. Moreover, the adhesive availability must be taken into consideration.
The same inventor, in U.S. Pat. No. 5,757,765, further discloses an improved structure to the invention disclosed in the Taiwan Patent Publication No. 312232, in which an annular adhesive sheet is used to replace the adhesive applied to the inner annular portion of the compact disc. However, the protective film still has a complicated shape at its inner rim portion and suffers the above-mentioned first drawback of the structure disclosed in the Taiwan Patent Publication No. 312232.